This study compared hypertrophy of the left quadriceps femoris (QF) after sedentary subjects trained 2 days a week for 9 weeks using electrical stimulation or voluntary effort. Each day, 3 to 5 sets of 10 lengthening and shortening actions were performed. Maximal effort was used for voluntary training. Electrical stimulation evoked tetanic force in 50% or more of the QF. Muscle cross-sectional area, determined by MR imaging, showed a group x time x leg interaction (p < 0.05). This reflected a 10% increase for the left QF with electrical stimulation as compared to the 4% increase after voluntary training. The right, untrained QF did not change in size (p > 0.05) after either intervention. Voluntary and electrical stimulation trainees, respectively, showed 25 and 56% increases (p < 0.05) in training torque. The results suggest that voluntary effort limits hypertrophy early in resistance training, as done in this study.
(C) 1995 National Strength and Conditioning Association